1. Field of the Invention
The present invention generally relates to mobile communication networks and systems.
Detailed descriptions of mobile communication networks and systems can be found in the literature, in particular in Technical Specifications published by standardisation bodies such as in particular 3GPP (3rd Generation Partnership Project).
2. Description of the Prior Art
In a mobile communication system, a Mobile Station (MS) or User Equipment (UE) has access to mobile services offered by a Core Network (CN) via an Access Network (AN).
Typical examples of mobile communication systems are 2G systems such as in particular GSM (Global System for Mobile communications) and 3G systems such as in particular UMTS (Universal Mobile Telecommunication System).
There are different types of mobile services such as in particular CS based services (where CS stands for Circuit Switched), PS based services (where PS stands for Packet Switched), or IP based services (where IP stands for Internet Protocol) such as for example IMS based services (where IMS stands for IP Multimedia Subsystem). Mobile services are offered by a Core Network (CN) therefore comprising different domains and subsystems such as in particular CS domain, PS domain, and IMS subsystem.
Mobile services have traditionally been delivered to Mobile Stations via an Access Network corresponding to a Radio Access Network RAN, allowing relatively high mobility but at relatively high cost for the users.
Typical examples of RAN are GERAN (GSM/EDGE Radio Access Network, where EDGE stands for Enhanced Data rates for GSM Evolution) and UTRAN (UMTS Terrestrial Radio Access Network).
Now, there is an evolution towards Fixed Mobile Convergence, allowing mobile services to be delivered to users at lower cost in environments requiring lower mobility, such as in particular indoor environments.
For Fixed Mobile Convergence with services provided by a Mobile Core Network, two main technologies compete each other: UMA/GA technology based on WiFi/Bluetooth access points, and 3G femto-cells i.e. 3G cells whose coverage is adapted to residential market. Both use access points/cells that are connected through DSL/Broadband lines and Public Internet.
A description of UMA/GA (Unlicensed Mobile Access/Generic Access) technology can be found in particular in UMA/3GPP specifications.
Generic Access to the A/Gb interfaces (i.e. standardized interfaces defined for GERAN A/Gb mode) also called “A/Gb mode” Generic Access, is specified in particular in 3GPP TS 43.318 and TS 44.318.
Generic Access to the Iu interface (i.e. standardized interface defined for UTRAN) also called “Iu mode” Generic Access, is disclosed in particular in 3GPP TR 43.902 (Enhanced Generic Access Network Controllers Study (EGAN)).
Generic Access to the Iu interface (“Iu mode GAN”) is an extension of UMTS mobile services that is achieved by tunnelling Non Access Stratum (NAS) protocols between the user equipment (MS) and the Core Network over an IP network. Iu-mode GAN is a complement to traditional GSM/GPRS/UMTS radio access network coverage.
Iu mode GAN architecture as disclosed in 3GPP TR 43.902 is briefly recalled, in relation with FIG. 1.
GAN architecture includes a Generic Access Network Controller GANC. The functionality of GANC defined for A/Gb mode GA is expanded so as to appear to the CN as a UTRAN Radio Network Controller (RNC). As for A/Gb mode GA, the GANC includes a Security Gateway (SEGW) that terminates secure remote access tunnels from the MS, providing mutual authentication, encryption and data integrity for signalling, voice and data traffic.
A Generic IP Access network provides connectivity between the MS and the GANC. The IP transport connection extends from the GANC to the MS. A single interface, the Up interface, is defined between the GANC and the MS. Functionality is added to this interface, over that defined for A/Gb GA mode, to support the Iu-mode GAN service.
The GANC is interconnected with the CN via the standardized interfaces defined for UTRAN, including in particular Iu-cs interface for CS services as defined in 3GPP TS 25.410, and Iu-ps interface for PS services as defined in 3GPP TS 25.410.
Transaction control (e.g. CC, SM) and user services are provided by the Core Network (e.g. MSC/VLR and the SGSN/GGSN).
Control and User Plane GAN architecture for CS and PS domain are specified in 3GPP TR 43.902. For example PS domain Control Plane GAN architecture is recalled in FIG. 2, and PS domain User Plane GAN architecture is recalled in FIG. 3.
The main features of the GAN PS domain control plane architecture are as follows:                The underlying Access Layers and Transport IP layer provides the generic connectivity between the MS and the GANC.        The IPsec layer provides encryption and data integrity.        TCP provides reliable transport for the GA-RRC between MS and GANC.        The GA-RC manages the IP connection, including the GAN registration procedures.        The Generic Access Radio Resource Control (GA-RRC) protocol performs functionality equivalent to the UTRAN RRC protocol, using the underlying Up session managed by the GA-RC. Note that GA-RRC includes both CS service and PS service-related signaling messages.        The GANC terminates the GA-RRC protocol and inter-works it to the RANAP protocol over the Iu-ps interface.        NAS protocols, such as for GMM, SM and SMS, are carried transparently between the MS and SGSN.        The Iu-ps signalling transport layer options (both ATM and IP-based) are defined in 25.412.        
The main features of the GAN PS domain user plane architecture are as follows:                The underlying Access Layers and Transport IP layer provides the generic connectivity between the MS and the GANC.        The IPsec layer provides encryption and data integrity.        The GA-RRC protocol operates between the MS to the GANC transporting the upper layer payload (i.e. user plane data) across the Up interface.        PS user data is carried transparently between the MS and CN.        The GANC terminates the GA-RRC protocol and inter-works it to the Iu-ps interface using GTP-U.        
Both UMA/GA and femto-cell technologies require security on the air and over the Public Internet. Both technologies consist in radio access networks (and possibly more) that are connected to a Core Network.
A solution where a common GANC can be reused for femto-cells technology and UMA/GA technology is disclosed in Kineto white paper entitled “The Case for UMA-Enabled Femtocells”.
In this solution, the GANC is connected to the Core Network via Iu-cs and Iu-ps interfaces. Moreover, the femto-cell equipment is connected to the GANC via a modified Up interface, which is the “air interface” of the “Iu-GAN Enhanced GAN” solution described in 3GPP TR 43.902 v1.1.0. The femto-cell equipment performs the termination of UMTS Uu interface, MAC, RLC, RRC and PDCP layers as well as emulating a GAN client interfaced via modified Up.
In terms of security, both UMA/GA and UMTS femto-cells technologies require security on the air and over the Public Internet.                In UMA (GAN), the user is authenticated via a terminal-network procedure and security is achieved via an IPsec tunnel between the terminal and the GANC Security Gateway, the Wifi/Bluetooth access point acting as a simple relay.        In 3G femto-cells, the air interface is a legacy UMTS interface and the ciphering function is in the RNC function (RLC layer). In solutions where the RNC function is located in the femto-cell equipment, the air interface is ciphered but the femto-cell/network path must also be ciphered.        
For that purpose, the femto-cell equipment must be authenticated to guarantee a safe connection to the terminals. The solution consists in considering the femto-cell equipment as a GAN subscriber: the femto-cell equipment includes a SIM/USIM for authentication and operates as IPsec termination for ciphering Up interface that is carried over the Public Internet.
Finally, the appropriate GANC node is “discovered” via legacy UMA (GAN) procedures. This mechanism allows to minimize the Mobility Management signaling in the Core Network and to perform load-sharing among GANC nodes.